6-nylon and 66-nylon are resins having excellent moldability, heat resistance, chemical resistance and mechanical properties and, therefore, have been extensively used in various applications such as automobile and vehicle-related parts, electric and electronic parts, household or business electric equipment-related parts, computer-related parts, facsimile or copier-related parts, mechanical parts, packaging materials and fishing materials. In particular, in the application field of automobile and vehicle-related parts, intensive studies have been made to apply these nylons to under-hood parts for automobiles such as intake manifold, hinged clip (hinged molded product), binding band, resonator, air cleaner, engine cover, rocker cover, cylinder head cover, timing belt cover, gasoline tank, gasoline sub-tank, radiator tank, inter-cooler tank, oil reservoir tank, oil pan, electric power steering gear, oil strainer, canister, engine mount, junction block, relay block, connector, corrugated tube and protector.
These under-hood parts for automobiles have been required to have a higher strength in order to meet various requirements owing to a complicated structure of the parts and a reduced thickness thereof for the purpose of weight reduction. Among these under-hood parts for automobiles, the intake manifold having a larger size is more susceptible to a weight-reduction effect than the other automobile parts by decreasing a thickness thereof. However, the intake manifold must be kept safe without damage thereto even when an internal pressure thereof is increased owing to backfire of an engine, etc. Therefore, at the present time, reduction in thickness of these parts such as the intake manifold is possible only to a limited extent.
In recent years, as the material for resin intake manifolds, there has been mainly used glass fiber-reinforced 6-nylon, and the intake manifolds have been mainly produced therefrom by a vibration-welding method. Also, there has been proposed the resin intake manifold produced by using 56-nylon instead of the 6-nylon (for example, refer to Patent document 1). However, the 56-nylon tends to be insufficient in vibration-welding strength, and further deteriorated in retention heat stability, and, therefore, is unsuitable for large-size molded products requiring a long molding cycle time such as intake manifolds. For this reason, it has been demanded to provide polyamide resins having more excellent vibration-welding strength and retention heat stability than those of 56-nylon.
There is also known a 56/66 nylon containing a smaller amount of 56-nylon and a larger amount of 66-nylon (ratio 56/66=0.5/99.5 to 40/60 mol % and preferably 0.5/99.5 to 10/90 mol %) (for example, refer to Patent document 2). Since the polyamide resin of this type aims at suppressing gelation of 66-nylon while maintaining functions of 66-nylon, the amount of 56-nylon added thereto is small. Therefore, it is considered that the polyamide resin exhibits only a vibration-welding strength substantially identical to that of 66-nylon, though it is not clearly known. Thus, in order to apply the polyamide resin to production of large-size thin-walled molded products, further improvement in properties thereof are required.
Hinged molded products have been frequently used for under-hood parts for automobiles. At the present time, the hinged molded products requiring a high heat resistance have been produced from 66-nylon, whereas the hinged molded products requiring a high toughness have been produced from 6-nylon. The 66-nylon has a melting point as high as 264° C. and a high crystallinity and, therefore, is slightly low in toughness. Therefore, the hinged molded products produced from the 66-nylon tend to suffer from breakage upon bending. On the other hand, the 6-nylon has a lower crystallinity than that of the 66-nylon and, therefore, exhibits a good toughness. However, the melting point of the 6-nylon is 224° C., i.e., much lower by 40° than that of the 66-nylon.
With the recent increasing tendency that hinged parts have a complicated shape, it has been demanded to provide polyamide resins having a more excellent hinge property than that of 6-nylon. Further, with the reduction or compactness in size of an engine room of automobiles, it has been demanded to provide polyamide resins having a higher heat resistance (melting point). In addition, these polyamide resins are required to have a rigidity (bending modulus) identical to or higher than that of 6-nylon.
As the method of improving a hinge property of hinged molded products, there is known the method of blending the polyamide resin with a boron nitride powder and an aliphatic carboxylic acid derivative (for example, refer to Patent document 3). However, it is considered that the resin composition of this type fails to exhibit an improved heat resistance (melting point).
Also, there is known the method of blending the polyamide resin with a polyolefin such as polypropylene and polyethylene (for example, refer to Patent document 4 However, the polyamide resin composition of this type tends to be deteriorated in heat resistance (melting point) or mechanical properties such as bending modulus as compared to those of the polyamide resin.
As the polyamide resin satisfying both the above hinge property and the heat resistance (heat-deforming temperature), there is known the polyamide resin composition composing an aromatic polyamide resin, a modified polyolefin, and an epoxy-containing polymer or an epoxidated diene-based block copolymer (for example, refer to Patent documents 5 and 6). However, the bending modulus of the polyamide resin composition of this type is as low as about 1500 to 1900 MPa which is considerably deteriorated as compared to a bending modulus of ordinary 6-nylon (about 2550 MPa) and that of ordinary 66-nylon (about 2940 MPa). Therefore, the polyamide resin composition tends to be deficient in rigidity as an important mechanical property. For this reason, it has been demanded to provide polyamide resins capable of exhibiting more excellent hinge property and heat resistance (melting point) than those of 6-nylon and simultaneously having a rigidity (bending modulus) identical to or higher than that of 6-nylon.
Also, as the raw material of the polyamide resin, there are used so-called fossil materials such as naphtha. However, with the recent requirements for prevention of global warming by suppressing discharge of carbon dioxide as well as establishment of recycling type society, it has been demanded to replace the material for production of the polyamide resins with a biomass-derived raw material. More specifically, it has been required that the polyamide is produced from such a raw material having a high biomass ratio (ratio of the biomass-derived material to the whole raw materials used for production of the polyamide resin).
The use of the biomass-derived material has been extensively demanded in various application fields including not only automobiles, but also electric and electronic parts, films and filaments. Specific examples of these parts include vibration-welded molded products such as the above intake manifold having an excellent vibration welding strength, hinged molded products and binding bands having an excellent low-temperature toughness, and filaments having an excellent transparency.
Known polyamide resins produced by polymerizing the biomass-derived material include, for example, 56 nylon. The 56 nylon has substantially the same heat resistance and mechanical properties as those of 6 nylon or 66 nylon. As the method for production of the 56 nylon, there are known the method of heat-polycondensing diaminopentane with adipic acid (for example, refer to Patent document 7), and the method of preparing a salt of diaminopentane and adipic acid and then heat-polycondensing the salt (for example, refer to Patent document 8). However, as described above, the 56 nylon tends to be deteriorated in vibration-welding strength and retention heat stability. For this reason, it has been demanded to develop polyamide resins which can be produced by polymerizing a biomass-derived raw material, and are capable of providing binding bands having an excellent low-temperature toughness and filaments having an excellent transparency. However, there are conventionally unknown hinged molded products produced from the 56 nylon.    Patent Document 1: Japanese Patent Application Laid-open (KOKAI) No. 2004-269634    Patent Document 2: PCT Pamphlet No. 93/00385    Patent Document 3: Japanese Patent Application Laid-open (KOKAI) No. 7-82474.    Patent Document 4: Japanese Patent Application Laid-open (KOKAI) No. 9-249808.    Patent Document 5: Japanese Patent Application Laid-open (KOKAI) No. 9-124934    Patent Document 6: Japanese Patent Application Laid-open (KOKAI) No. 2000-204243    Patent Document 7: Japanese Patent Application Laid-open (KOKAI) No. 2003-292612    Patent Document 8: U.S. Pat. No. 2,130,948